The invention relates to a feeder, more especially a sheet feeder, comprising firstly a suction device which is placed over a stack of items to be fed, and has a separating device with at least one telescoping and preferably vertically reciprocable lifting suction holder, which when a sucker is covered over is able to be retracted against the action of a returning force by the action of vacuum present at such sucker, and secondly a conveyor device which has at least one reciprocating entraining sucking device and is adapted to have such item transferred to it from the separating device lifting such item from said stack.
In a sheet feeder of this type it is only possible for the lifting suction holders, which as a rule are arranged in the vicinity of the rear edge of the stack, to take the first sheet (or other item) from the stack, when the entraining suction holders have moved the sheet or other item, which has previously been transferred, clear of the field of action of the lifting suction holders. The consequence of this is that the retracted part of the lifting suction holders has to dwell in such retracted position after transfer of the sheet for a certain length of time. Since for the transfer of a sheet the vacuum present at the sucker of the lifting suction holders has to be interrupted, it is necessary for the part of the suction holders which may be moved outwards to be held, against the force acting in the outward direction, in the retracted position. For this purpose use has so far been made of mechanical latches which are actuated by means of an actuating device secured to the machine frame. A disadvantage in this respect is not only the wear of the mechanical latches, but also the trouble of adjusting them.
In this connection it has in fact to be assumed that the lifting suction holders are able to be adjusted in height and in the case of such vertical adjustment having to be performed, there will also be the trouble of resetting the actuating device secured to the frame. Prior art feeders will thus be seen to be overly complex in design and not sufficiently simple to operate.